Hello,I'm so new to electronics. I have a ch-926 coin acceptor, an Arduino Uno (with ethernet shield) and 12V,2A adapter. Is it possible for me to power arduino with this adapter and power the coin acceptor from Arduino? Would it damage the coin acceptor, Ethernet shield or Arduino?

Arduino 5V regulator is only good for 800mA max, and less from a 12V source, the regulator will overheat.You can supply 12V to arduino, and run12V in parallel to the coin acceptor with its own 5V regulator if needed.Connect grounds to provide common reference point.

Thank you for your answer. Coin acceptor needs 12V but i am not sure about the mA needed. I want to make a prototype but obviously there should be just one power unit to power the system. What would you suggest i do?

, then power it from the 12v power supply.You can also power the arduino from that same 12v power supply. Put in several capacitors to help provide isolation.If you had 2 or 3 general purpose diodes, I would put 2 or 3 in series to drop the 12v down a couple volts. Arduino will work with 12v on the Vin, but is happier with 7v.

Best advice, keep all other devices power supplies separated from the arduino.I don't know this coin-validator , but i presume it uses pulse signals for the accepted coins instead of any protocol communications.

Use separate powersupply for power and use opto-couplers between signal wires and arduino.

I think the arduino is ok with 12V but NOT with 12.8V, so better NEVER use higher power for arduino then lets say 9V. And never supply any voltage to any hooked up device from the arduino.I think you can even damage your board if you start driving shhiitloads of LED's without extra external powersupply.

I found out i needed a desktop powersupply with +12, -12, +5, -5 and 0/ground to do all these experiments .